Data communication over power lines

ABSTRACT

A system for receiving and processing signals received from a plurality of endpoints. Each endpoint includes an endpoint transmitter in electrical communication with a power distribution line within a power distribution system. The system comprises a power line coupler. A substation receiver is in electrical communication with the power line coupler. A substation circuit is in electrical communication with the substation transceiver. The substation circuit is configured to simultaneously demodulate signals received from the plurality of different endpoints.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/760,041,filed Jun. 8, 2007, which is a continuation of application Ser. No.10/626,495, filed Jul. 24, 2003, now U.S. Pat. No. 7,236,765, whichapplications are incorporated herein by reference in their entirety

INCORPORATION BY REFERENCE

The entire disclosures of the following are hereby incorporated byreference: U.S. application Ser. No. 10/626,465 entitled “Power LineCommunication System Having Time Server” filed on Jul. 24, 2003, whichissued on Feb. 20, 2007 as U.S. Pat. No. 7,180,412; U.S. applicationSer. No. 10/626,496 entitled “Locating Endpoints in Power LineCommunication System” filed on Jul. 24, 2003; U.S. application Ser. No.10/627,397 entitled “Endpoint Processing and Communication System” filedon Jul. 24, 2003, which issued on Feb. 14, 2006 as U.S. Pat. No.6,998,963; U.S. application Ser. No. 10/627,587 entitled “EndpointTransmitter and Power Generation System” filed on Jul. 24, 2003, whichissued on Sep. 5, 2006 as U.S. Pat. No. 7,102,490; and U.S. applicationSer. No. 10/627,590 entitled “Endpoint Event Processing System” filed onJul. 24, 2003, which issued on Dec. 5, 2006 as U.S. Pat. No. 7,145,438.

TECHNICAL FIELD

This invention relates generally to data communication and moreparticularly to data communication over power lines.

BACKGROUND

As is true with most companies, utility companies are striving to reduceoverhead costs, while providing more convenience to customers. Forexample, electric companies are migrating from costly and time-consumingmanual methods of determining the amount of power consumed by customersof the power company. Traditionally, a person periodically came to thecustomer's home, and requested entry to read the consumer power usagefrom a power meter. This type of process was costly, slow, and intrusiveto their customers.

Newer systems provide some level of remote communication between anendpoint such as an electrical meter and a central location. One suchsystem is an automated meter reading (AMR) system that utilizes a powerline to establish a data link between a concentrator and endpoint meterreading units positioned downstream from the substation. Theconcentrator typically includes a transmitter for transmitting controlinformation to the endpoint and a receiver for receiving data such aswatt-hour information from the endpoint. The endpoint includes atransmitter, a receiver, and electronics or other circuitry for readingthe meter. Other remote meter reading and data communication systemsthat use modems, radio frequency signals, or PLC signals can communicatewith only one endpoint at a time and thus have limited capacity.

These current systems have shortcomings. For example, the capacity ofsuch systems is limited because the concentrator (or other centralprocessing system if modems or RF are used) can receive signals fromonly one endpoint at a given time. This limitation provides a bottleneckthat limits the processing power and flexibility of the system.Additionally, it limits the number of endpoints that the concentratorcan communicate within a 24-hour period and hence limits the number ofendpoints that can be connected downstream from any given concentrator.

The systems also have little scalability. This limitation is caused bytwo factors including the limited number of endpoints that can beconnected downstream from a concentrator and by the manual programmingrequired every time that an endpoint is added to the system.

Other shortcomings of current AMR and other power line datacommunication systems relate to reliability, flexibility, andscalability. For example, the system needs to be manually programmedeach time an endpoint is added. In another example, if there is a poweroutage, automated meter reading systems generally require polling of theendpoints to determine which ones are still operational. This polling isslow and consumes processing and communication resources. Furthermore,current systems generally do not have the capability of reestablishingcommunication between an endpoint and an alternative concentrator if thecommunication link between the concentrator and the endpoint isdisconnected by intentionally taking the substation off line, through apower failure.

SUMMARY

In general terms, the present invention relates to a system forbi-directional communication over a power distribution system havingpower distribution lines.

One aspect of the invention relates to a system for receiving andprocessing signals received from a plurality of endpoints. Each endpointincludes an endpoint transmitter in electrical communication with apower distribution line within a power distribution system. The systemcomprises a power line coupler. A substation receiver is in electricalcommunication with the power line coupler. A substation circuit is inelectrical communication with the substation transceiver. The substationcircuit is configured to simultaneously demodulate signals received fromthe plurality of different endpoints.

Another aspect of the invention relates to a method of processingsignals received from a plurality of endpoints over power distributionlines. The method comprises obtaining a plurality of signals from apower distribution line, each signal corresponding to a differentfrequency bandwidth; and simultaneously demodulating the pluralitysignals.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating one link of a power distributionnetwork over which data is communicated between a distributionsubstation and an endpoint according to one possible embodiment of thepresent invention.

FIG. 2 is a block diagram illustrating a portion of a power distributionnetwork over which data is communicated between a distributionsubstation and an endpoint according to one possible embodiment of thepresent invention.

FIG. 3 is a schematic illustrating a substation controller and powerline coupler according to one possible embodiment of the presentinvention.

FIG. 4 is a block diagram illustrating a hierarchy of data channels asthey are demodulated according to one possible embodiment of the presentinvention.

FIG. 5 is a block diagram illustrating a circuit for processing datareceived at a substation transceiver according to one possibleembodiment of the present invention.

FIGS. 6A-6D is a block diagram illustrating a digital signal processingcircuit for demultiplexing and demodulating a plurality of data channelsaccording to one possible embodiment of the present invention.

FIG. 7 is a block diagram illustrating components of a substationtransceiver for transmitting a signal onto a power distribution networkaccording to one possible embodiment of the invention.

FIG. 8 is a block diagram illustrating a digital signal processingcircuit for demodulating a transmission signal fed back into asubstation transceiver according to one possible embodiment of thepresent invention.

FIG. 9 is a flowchart illustrating operation of at least a portion ofthe commands programmed into a computer illustrated in FIG. 5.

DETAILED DESCRIPTION

Various embodiments of the present invention will be described in detailwith reference to the drawings, wherein like reference numeralsrepresent like parts and assemblies throughout the several views.Reference to various embodiments does not limit the scope of theinvention, which is limited only by the scope of the claims attachedhereto. Additionally, any examples set forth in this specification arenot intended to be limiting and merely set forth some of the manypossible embodiments for the claimed invention.

FIG. 1 is a block diagram of one link of an electric distribution system100 distributing power between a distribution substation and a customerdevice at the power consumer's site. An electrical distribution system,or distribution plant as it is sometimes referred to, is that part of anelectric power system that receives power from a power generator viahigh-voltage transmission lines, reduces or steps down the voltage, andthen distributes the power to an endpoint at the premise of an energycustomer. Within the electrical distribution system, distribution linestypically conduct electricity from the distribution substation to theendpoints. Distribution lines typically consist of underground cable,aerial cable, or overhead open-wire conductors carried on poles, or somecombination of them.

There may be multiple layers of distribution substations connected inseries between the power generation and the endpoint, wherein eachconsecutive distribution substation further steps down the voltage ofthe electricity being transmitted. Additionally, the power generators,distribution substations, and endpoints are commonly organized in anetwork where various generators supplying power can be taken on or offline and the distribution substation through which a particular endpointreceives its electricity can be changed, all without a loss orinterruption of power.

Distribution transformers are ordinarily connected in the distributionline between the distribution substation and the endpoint, which thedistribution transformers serve to further step-down the voltage to alevel that is used by consumers. These step-down transformers, oftenreferred to as pole transformers, supply a consumer or group ofconsumers over a secondary circuit. Each consumer is connected to thesecondary circuit through its service leads and meter.

The distribution substation 102 shown in FIG. 1 provides power to acustomer device or endpoint 104 via a distribution line 106. Thedistribution line 106 may be coupled to one or more step-downtransformers before reaching the customer premise. The distribution line106 provides the power necessary to operate electrical devices, locatedat the endpoint 104, which is a device at the customer premise.Endpoints are discussed in U.S. application Ser. No. 10/627,397 entitled“Endpoint Processing and Communication System” filed on Jul. 24, 2003,which issued on Feb. 14, 2006 as U.S. Pat. No. 6,998,963, the entiredisclosure of which is hereby incorporated by reference.

For a variety of reasons, it may be desirable to communicate informationfrom the distribution substation 102 to one or more endpoints 104 at aparticular customer premise. For example, it may be desirable to controlor monitor a meter-reading device, which is installed at a customerpremise to determine the power consumption at that customer premise.Additionally, control information could provide the ability to controlor alter the operation of the meter-reading device and/or individualloads at the customer premise. Utility companies often provide acustomer with a power rate discount if the customer agrees to allow fora temporary adjustment of their consumption. For example, a powercompany may provide a customer with a rate discount where the customeragrees to allow the power company to temporarily adjust or terminatetheir power consumption for certain nonessential power consumingdevices, such as water heaters, swimming pool heaters, air conditioners,etc. during peak operation. This allows the utility company to limit thepeak power consumption when necessary, hereinafter referred to as “loadcontrol.”

Other more general information, which is not necessarily to “control”customer devices, also can be provided via the power distribution lines.These general information signals are transmitted in the same manner assignals intended to control a customer device. Such general informationsignals include information to display or store the price of power atthe customer premise, the date and time, the temperature or otherinformation capable of being received and translated at the customerpremise. For example, the time displayed on an electronic device at thecustomer premise could be periodically adjusted to display an accuratetime as transmitted by the utility station.

Various embodiments of the apparatuses and methods disclosed hereincommunicate control signals and general information signals to endpoints104 via the distribution line 106 to control customer devices andprovide more general information to the customer. Information from thecustomer device also may be sent via the distribution line 106 to thedistribution substation 102, thereby creating a two-way controlinformation communication link via the distribution line 106. Theaforementioned examples of control signal applications where controlsignals (and/or general information signals) are provided by thedistribution substation to an endpoint 104 are merely representative ofthe various uses that such control signals provide. Therefore, theexamples provided throughout the application are illustrative in nature,as the invention is not limited to any particular control signal use.

In order to provide control information at the distribution substation102, a substation controller 108, which includes a substationtransceiver, is used to drive the control signals along the distributionline 106 in the direction represented by the arrow 110. An endpointtransceiver 112 at the customer device 104 is configured to recognizethe control signals transmitted by the substation controller 108.Similarly, the substation controller 108 receives information, such as apower consumption reading, from the endpoint transceiver 112 in thedirection represented by arrow 118.

The control information communications link 100 shown in FIG. 1therefore provides a full-duplex or bi-directional communication linkbetween the distribution substation 102 and the endpoint 104, which istypically located at a customer premise. Full duplex in this senserefers to simultaneous communications in both directions, although theinformation sent in one direction may travel at a speed different fromthat of the information provided in the opposite direction. Thisfull-duplex communication link via the distribution line 106 providesfor reliable transmission of control information, without the need foradditional wiring, thereby minimizing cost and increasing dataintegrity.

Referring now to FIG. 2, a block diagram of a power distribution system200, which is substantially similar to the electrical distributionsystem 100 described above. In this exemplary embodiment, generatingstation 202 provides the bulk power to downstream distributionsubstations 102 via high-power transmission lines 203. At least one ofthe distribution substations 102 includes the substation controller 108.As can be seen by the example of FIG. 2, the substation controller 108can simultaneously communicate data via the distribution lines 106 tomultiple endpoints 104 residing in multiple customer premises. Thecontrol information can pass through transformers 210, and ultimately toa particular endpoint 104 located at a customer premise. A plurality ofendpoints 104 located at different customer premises may be serviced bya particular transformer 210. Furthermore, a single customer premisesuch as site 212 may include a plurality of different customer devicesor endpoints 104. The transfer of control information from a substationcontroller 108 to a great number of endpoint transceivers at differentendpoints 104 is very useful and cost effective. In various embodiments,one or more of the distribution substations 102 may include thesubstation controller 108 for communicating with endpoints 104 locateddownstream from the distribution substation 102. In other embodiments,the substation controller 108 is located at points that are upstreamfrom multiple endpoints 104 other than a distribution substation 102.

FIG. 3 illustrates the distribution substation 102 and one possibleembodiment of the connection of the substation controller 108 to thedistribution line 106. In this exemplary embodiment, the distributionline 106 interfaces with a main transformer 300 that providesthree-phase power (ϕA, ϕB, and ϕC) and includes three distribution lineconductors 302, 304, and 306, one for conducting each phase of thepower. The first conductor 302 conducts ϕA, the second conductor 304conducts ϕB, and the third conductor 306 conducts ϕC.

A metering loop 307 has three metering lines 314, 316, and 318 thatinterface with the three distribution line conductors 302, 304, and 306,respectively. The metering line 314 interfaces with the distributionline conductor 302 through a current transformer 308, the metering line316 interfaces with the distribution line conductor 304 through acurrent transformer 310, the metering line 318 interfaces with thedistribution line conductor 306 through a current transformer 312.

The substation controller 108 has three inputs 327, 329, and 331 forreceiving data from the endpoint transceivers 112 and one output 337 forsending data to the endpoint transceivers, and includes a substationprocessing unit 332 and an amplifier 336. The three inputs 327, 329, and331 interface with the metering loop 307 through current transformers320, 322, and 324, respectively. Specifically, a first input has a line326 that is coupled to the metering line 314 through a currenttransformer 320, a second input has a line 328 that is coupled to themetering line 316 through a current transformer 322, and a third inputhas a line 330 that is coupled to the metering line 318 through acurrent transformer 324.

In this exemplary embodiment, signals transmitted by an endpointtransceiver 112 connected to the first distribution line conductor 302,are communicated over the distribution line conductor 302, the meteringline 314, the input line 330, and into the first input 327 of thesubstation controller 108. Signals transmitted from endpointtransceivers 112 connected to the second and third distribution lineconductors 304 and 306 are fed to the substation controller 108 throughinputs 329 and 331, respectively, following similar paths alongdistribution line conductors 304 and 306, respectively, metering lines316 and 318, respectively, and input lines 328 and 330, respectively.

The substation processing unit 332 has a single output that feedssignals for downstream communication to the endpoint transceivers 112.This downstream signal from this single output is input to the amplifier336. The amplifier 336 then outputs the downstream signal from thesubstation controller 108 to a power line coupler 337, which is formedby an impedance matching unit 338 and capacitors 340, 342, and 344.

The identical signal is then communicated from the impedance matching338 onto each of the distribution line conductors 302, 304, and 306through the capacitors 340, 342, and 344, respectively. The impedancematching unit 338 matches the impedance between the distribution lineconductors 302, 304, and 306 and the amplifier 336. The capacitors 340,342, and 344 electrically isolate the impedance matching unit from thedistribution line 106.

In this exemplary embodiment, the substation controller 108 transmitsits command to all of the downstream endpoint transceivers 112. In analternative embodiment, the substation controller 108 can address adownstream signal to a particular endpoint transceiver 112.

In yet another possible embodiment, the substation controller 108 canshift the phase of the signal transmitted onto each of the distributionline conductors 302, 304, or 306 so that each conductor conducts asignal having a different phase. If the signal bleeds from onedistribution line conductor 302, 304, or 306 to another distributionline conductor 302, 304, or 306, the signals tend to cancel each otherbecause the electricity conducted on each of the distribution lineconductors 302, 304, or 306 is out of phase by about 120°. Shifting thephase of the signal transmitted by the substation controller 108 reducesthis cancellation when a signal bleeds from one distribution lineconductor 302, 304, or 306 to another distribution line conductor 302,304, or 306.

As explained in more detail herein, the substation processing unitcommunicates with a central office 334 via a data network 346. Invarious embodiments, the data network 346 is established using asuitable means for data communication. Examples, include the Internet,an Intranet, a wide area network, a local area network, satellite,microwave, and a modem interfacing with a plain old telephone line(POTS)

Additionally, other structures may have alternative structures andmethods for retrieving a data signal from the distribution line 106, fortransmitting a data signal onto the distribution line 106, andprocessing the signals in the substation controller 108. For example,the substation controller 108 might be broken into a separate receiverand transmitter.

Referring to FIG. 4 and as explained in more detail herein, the endpointtransceivers 112 disclosed in the exemplary embodiment modulate thesignals that they transmit to the substation controller 108 usingfrequency shift keying and transmits its signal to the substationcontroller 108 located at the distribution substation 102. In onepossible embodiment of this modulation scheme, each endpoint transceiver112 sends its signal within a channel 402 having a predeterminedbandwidth of about 36 Hz, from about 970 Hz to about 1,006 Hz. Whendemodulating the signals received over the 36 Hz channel 402, thesubstation controller 108 separates the signals into about 72sub-channels 404. It then separates each of the sub-channels 404 intoabout 125 sub-sub-channels 406. Each of the sub-sub channels 406 isassigned to a different downstream endpoint transceiver 112 andcorresponds to a signal having a bandwidth of about 4 Hz.

In the exemplary embodiment, each endpoint transceiver 112 is assignedpredetermined bandwidth of about 4 Hz, and each assigned predeterminedbandwidth within the main channel 402 is mutually exclusive from oneanother. Given this configuration, the substation controller 108 has thecapacity to receive signals from about 9,000 separate downstreamendpoint transceivers 112. Additionally, the predetermined bandwidth foreach sub-sub-channel 406 includes a base frequency to which an endpointtransceiver 112 is assigned and any frequency to which the basefrequency is shifted when the endpoint transceiver 112 modulates asignal for transmission to the substation controller 108.

The distribution substation controller 108 demodulates each signalreceived from separate endpoint transceivers 112 substantiallysimultaneously, which provides significant advantages. For example, itincreases the capacity of the system because the substation controller108 does not have to delay reception of one signal from an endpointtransceiver 112 until the reception of the previous signal is completed.

As further explained herein, each distribution line 106 has three phasesand one distribution line conductor 302, 304, and 306 for each phase.The interface for each of the three distribution line conductors 302,304, and 306 receives one channel over each of the three distributionline conductors 302, 304, and 306. In one possible embodiment, eachchannel has a bandwidth of about 36 Hz, from about 970 Hz to about 1,006Hz. Accordingly, the substation controller 108 performs the demodulationscheme illustrated in FIG. 4 for each distribution line conductor 302,304, and 306 of the distribution line 106. This configuration gives thesubstation transceiver 106 the capacity to receive signals from up toabout 9,000 endpoint transceivers 112 on any one or combination of thethree distribution line conductors 302, 304, and 306.

There are many other additional embodiments in addition to thosedescribed herein. For example, an endpoint transceiver 112 cancommunicate with the substation controller 108 using any modulationscheme, including modulation schemes other than frequency shift keying,that permit simultaneous or substantially simultaneous demodulation ofsignals received from the endpoint transceivers 112. Additionally, otherbandwidths can be used within the apparatus and methods disclosedherein. For example, the channel 402 might include a frequency bandwidthother than 36 Hz and other than the range of 970 Hz to 1,006 Hz. Yetother embodiment will have the capacity to receive signals from fewerthan 9,000 endpoint transceivers 112 or more than 9,000 endpointtransceivers 112.

In alternative embodiments, the endpoint transceivers 112 communicateusing frequency bandwidths other than 4 mHz. For example, variousembodiments might use a frequency bandwidth of about 10 mHz or less,including frequencies of about 2 mHz, 6 mHz, or 8 mHz. Yet otherembodiments use frequency bandwidths other than 2 mHz, 4 mHz, 6 mHz, 8mHz, or 10 mHz. Still other embodiments might use frequency bandwidthsgreater than 10 mHz.

Referring to FIG. 5, the exemplary embodiment of the substationprocessing unit 332 includes four low pass filters 501, 503, 505, and507, four variable gain devices 508, 510, 512, 514, and 516, four highpass filters 509, 511, 513, and 515, a complex programmable logic device(CPLD) 530, four analog to digital (A/D) converters 518, 520, 522, and524, first and second digital signal processors (DSP) 536 and 538, twowindowed watch-dog circuits 544 and 546, a single board computer 540,flash memory 532, and a modem 542.

The CPLD 530 is programmed to include a clock 526, a variable gaincontroller 528, and four receive buffers 510, 512, 514, and 516 that areused to buffer the signals received from the distribution line that arebeing input to the first and second DSPs 536 and 538 for demodulation.As explained in more detail herein, the CPLD 530 may have additionalbuffers for various functions such as buffering data being transmittedby the substation controller 108. One type of CPLD that can be used ischip no. XC95144XL, which is manufactured by XILINX located inCalifornia, U.S.A.

The clock 526 provides a clocking signal to each of the A/D converters518, 520, 522, and 524. The variable gain controller 528 provides asignal to each of the variable gain devices 502, 504, 506, and 508. Inone possible embodiment, the variable gain devices 502, 504, 506, and508 are op amps that output a signal having an amplitude of about 2.5Volts.

The flash memory 532 stores the code for the first and second DSPs 536and 538. The flash memory 532 also stores an error log that recordserror signals generated by the first and second DSPs 536 and 538.

As explained in more detail herein, the first and second DSPs 514 and516 demodulate the signals received over the distribution line 106 usingfrequency shift keying. The second DSP 538 then outputs the demodulateddata into the signal board computer 540, which stores the data in thememory (not shown). One type of chip that can be used for the DSPs ischip no. TMS3206711, which is manufactured by Texas Instruments locatedin Texas, U.S.A.

In operation, an endpoint transceiver 112 generates a signal thatembodies data and transmits that signal over the distribution line 106.For exemplary purposes, the endpoint transceiver 112 is in electricalcommunication with and transmits its signal over the distribution lineconductor 302. The signal then propagates through the currenttransformer 308, along metering loop line 314, through currenttransformer 320, along input line 326, and into the first input 327.

The signal is conditioned by passing through the high pass filter 501,the first variable gain device 502, and the low pass filter 509. Thevariable gain device 502 is an amplifier that biases the signal apredetermined amount such as about 2.5 Volts. The high pass and low passfilters 501 and 509 isolate the signal and remove noise. The signal isconverted from analog to digital by the first A/D converter 518 andinput to the first buffer 510 programmed into the CPLD 530. The bufferedsignal is input to the first DSP 536. The first DSP 536 performs a firstportion of the operations to demodulate the signal and then passes thesignal to the second DSP 538, which completes the demodulation process.The demodulated signal is input to the single board computer 540.

Signals transmitted on the transmission conductor 304 similarlypropagate through the current transformer 310, along metering line 316,through current transformer 322, along input line 328 and input secondinput 329. The signals then propagate through the high pass filter 503,through the variable gain device 504, through the low pass filter 511,through the second A/D converter 520 and input the second buffer 512programmed into the CPLD 530. The signal then is processed by the firstand second DSPs 536 and 538, and input to the single board computer 540.

Signals transmitted on the distribution line conductor 306 alsosimilarly propagate through the current transformer 312, along meteringline 318, through current transformer 324, along input line 330 andinput second input 331. The signals then propagate through the high passfilter 505, through a variable gain device 506, through the low passfilter 513, through an A/D converter 522 and input the second buffer 514programmed into the CPLD 530. The signal then is processed by the firstand second DSPs 536 and 538, and input to the single board computer 540.

The first and second DSPs 536 and 538 monitor each of the distributionline conductors 302, 304, and 306 for each sub-sub-channel 406. Thus, ifan endpoint transceiver 112 is transmitting a signal on one of thesub-sub-conductors 302, 304, or 306 and the signal bleeds to the othertwo conductors, the substation controller 108 will receive threeseparate signals within the frequency band of the sub-sub-channel 406.The single board computer 540 then determines which of the signals hasthe greatest amplitude and discards data from the other two signals. Anadvantage of this embodiment is that a technician installing theendpoint transceiver 112 can quickly connect it to any of thedistribution line conductors 302, 304, or 306.

Signals transmitted by the substation controller 108 are fed back intothe substation controller 108 and recorded. This feedback provides ahistorical record of the data actually transmitted onto the distributionline 106. Because the transmitted signal propagates wherever power isdistributed, it is also transmitted to a 120 volt outlet in which apower supply (not shown) for the single board computer 540 is plugged. Asignal is picked up from the power supply, and is then processed similarto the signals that are transmitted on the distribution line 106 by theendpoint transceivers 112. More specifically, the signal is fed throughthe high pass filter 507, through the variable gain device 508, throughthe low pass filter 515, and then through the fourth A/D converter 524.The signal is then buffered 516 by the fourth buffer programmed in theCPLD 530 and input to the first and second DSPs 536 and 538 where it isdemodulated.

The first DSP 536 sends a watch-dog signal to the windowed watch-dogtimer 544 at a predetermined interval. If the windowed watch-dog timer544 does not receive a watch-dog signal within the predefined window, itgenerates and sends a reset signal to the first DSP 536. In one possibleembodiment, the window within which the windowed watch-dog circuit 544looks to receive a watch-dog signal is from about 0.7 seconds to about1.3 seconds. The second DSP 538 interfaces with the windowed watch-dogtimer 545 in a similar manner.

The single board computer 540 is a standard computer board 540 thatincludes a programmable processor, memory, and various inputs andoutputs. One type of single board computer that can be used in Model #EBCTXPLUS-5222B, which is manufactured by WinSystems located in Texas,U.S.A. The single board computer 540 communicates with the second DSP538 through a data bus 534. In the exemplary embodiment, the data bus534 is a universal asynchronous receive and transmit (UART) data busthat communicates according to the RS-485 data protocol. The second DSP538 includes a command processor or decoder that decodes commandsreceived from the single board computer 540 and then either processesthe command itself or relays the command to the first DSP 536, clock526, variable gain device controller 528, or other hardware or firmwareelement for execution.

Additionally, the single board computer 540 communicates to the outsideworld through a network interface 542. Examples of possible networkinterfaces include modems for communication over plain old telephonelines (POTS). Other examples, include hardware and drivers to supportcommunication using the Internet, an Intranet, a wide area network(WAN), a local area network (LAN), satellite, microwave, or any othertype of network connection that can be used for communicating data toremote locations, whether the communication is over hardwired lines oris wireless.

Although a certain hardware and software configuration is illustrated inthis exemplary embodiment for receiving and processing data signalsthere are many possible alternative embodiments and the invention can beembodied in any configuration of hardware and/or software that canreceive, demodulate, and demultiplex the signals.

Referring to FIGS. 4 and 6A, the signal output from the first D/Aconverter 518 and buffered in the first buffer 510 corresponds to themain channel 402, which in the exemplary embodiment has a bandwidth ofabout 36 Hz (970 Hz to 1006 Hz). The signal is input to the first DSP536, where it passes through a low pass filter 600, through a 100:1decimator 602 and then a high pass filter 604.

In one possible embodiment, the low pass filter 600 has a cutofffrequency of about 1090 Hz and prevents aliasing or the erroneousinterpretation of a high frequency component as a lower frequencycomponent as the signal is sampled. The 100:1 decimator 602 changes thesampling rate from about 250,000 samples per second (sps) to about 2,500sps. The 100:1 decimator 602 reduces the sampling rate by accumulating200 words. The high pass filter 604 has a cutoff frequency of about 906Hz and filters all frequencies below 906 Hz, including the 60 Hzcomponent from the alternating current conducted by the transmissionline 100.

The signal is then passed to first and second signal branches 606 a and606 b. Along the first signal branch 606 a, the signal passes through amixer 608 a that combines the signal with a cosine wave 610 having apredetermined frequency. In exemplary embodiment disclosed herein thecosine wave has a frequency of about 960 Hz, which is line locked to thepower distribution frequency of the 120/240V input for the SPU 332. Anadvantage of line locking the frequency of the cosine wave is that itwill vary with the frequency (about 60 Hz) of the alternating currentcarried by the distribution line 106, which is the carrier wave for thesignals transmitted by the endpoint transceivers 112. The signal thenpasses through a low pass filter 614 a and then a 12:1 decimator 616 a.In one possible embodiment, the low pass filter 614 a has a cutofffrequency of about 50 Hz and the 12:1 decimator 618 a changes thesampling rate from about 2500 sps to about 208.33 sps.

The signal passed to the second branch 606 b is processed in a similarmanner passing through a mixer 608 b, a low pass filter 614 b, and a12:1 decimator 618 b. In the exemplary embodiment, the only differencefor the processing in the first branch 606 a is that the mixer combinesthe signal with a sine wave having a frequency of about 960 Hz.

In the exemplary embodiment, the code for the 12:1 decimators 618 a and618 b are split between the first and second DSPs 536 and 538.Accordingly, the signals propagating along the first and second signalbranches 606 a and 606 b are passed from the first DSP 536 to the secondDSP 538 as they are being processed by the 12:1 decimators 616 a and 616b. In another possible embodiment, all of the demodulation stepsillustrated in FIG. 6A-6C are performed in a single digital signalprocessor so long as it has enough processing power and memory.

Referring to FIGS. 4 and 6B, the signal output by the 12:1 decimators616 a and 616 b are input into 72 parallel sub-channel signal branches,each parallel sub-channel signal branch corresponding a separatesub-channel 404. As it passes through each of the parallel sub-channelsignal branches, the signal transmitted along the first signal branch606 a passes through a bandpass filter 618 a, through a mixer 622 a, andinto a subtractor 628. In the exemplary embodiment, the bandpass filterhas a lower cutoff frequency of about 10 Hz and an upper cutofffrequency of about 10.5. The mixer 622 a mixes the signal with a cosinewave 624 having a predetermined frequency of about 9.8 Hz, which is linelocked to the power distribution frequency of the 120/240V input for theSPU 332.

Similarly, the signal transmitted along the second signal branch 606 bpasses through a bandpass filter 618 b, through a mixer 622 b, and intothe subtractor 628. The primary difference from the first signal branch606 a is that the mixer 622 b combines the signal with a sine wavehaving a frequency of about 9.8 Hz, which is line locked to the powerdistribution frequency of the 120/240V input for the SPU 332. Thesubtractor 628 then subtracts the signal processed along the secondsignal branch 606 b from the signal processed along the first signalbranch 606 a. The signal output from the subtractor 628 is passedthrough a low pass filter 630 and a 71:1 decimator 632. The low passfilter 630 has a cutoff frequency of about 0.7 Hz and further isolatesthe data signal. The 71:1 decimator further reduces the sampling ratefrom about 208.33 sps to about 2.93 sps.

In the exemplary embodiment, the bandpass filter 618 b has a lowercutoff frequency of about 10 Hz and an upper cutoff frequency of about10.5. The mixer 622 b mixes the signal with a sine wave 626 having apredetermined frequency of about 9.8 Hz, which is line locked to thepower distribution frequency of the 120/240V input for the SPU 332.

Each of the parallel sub-channel signal branches is substantially thesame as the illustrated block diagram for sub-channel 1. The primarydifference is that the frequency input to the mixer is incremented byabout 0.5 Hz for each successive sub-channel 404. The frequency input tothe mixer is line locked to the power distribution frequency of the120/240V input for the SPU 332. Similarly, the maximum and minimumcutoff frequencies for the bandpass filters 618 are increased by about0.5 Hz for each successive sub-channel 404. Thus, for example, thesecond sub-channel has a mixer frequency of about 10.3 Hz and thebandpass filter has cutoff frequencies of about 10.5 Hz and about 11.0Hz. In this exemplary embodiment, the seventy-second sub-channel has amixer frequency of about 45.3 Hz and the bandpass filter has cutofffrequencies of about 45.5 Hz and about 50.0 Hz.

Referring to FIGS. 4 and 6C, the signal output by the 71:1 decimator 632for each parallel sub-channel signal branch is input into 125 parallelsub-sub-channel signal branches. Each parallel sub-sub-channel signalbranch corresponds to a separate sub-sub-channel 406. Given thearchitecture in this exemplary embodiment, there are about 9000 parallelsub-sub channel signal branches.

The signal input to the first sub-sub-channel signal branch passesthrough a high pass filter 634, a mixer 636, and a low pass filter 642.In the exemplary embodiment, the high pass filter 634 has a cut offfrequency of about 0.198 Hz, and the mixer 652 combines the data signalwith a cosine wave 640 having a frequency of about 0.184 Hz, which isline locked to the power distribution frequency of the 120/240V inputfor the SPU 332.

After passing through the low pass filter 642, the data signal is outputto a first signal branch 644 and a second signal branch 646. The signalpassed to the first signal branch 644 is passed through a 44:1 decimator648, which decreases the sampling rate from about 2.93 sps to about0.0667 sps.

Referring to FIGS. 6C and 6D, the decimated signal passed into aheuristically correlated detector 652, which estimates the phase of thesignal received from the endpoint transceiver 112. The signal propagatesonto two signal paths 667 a and 667 b. On the first signal branch, thesignal is input to five multipliers 668 a-668 e. The first multiplier668 a mixes the signal with a cosine wave having a phase calculatedaccording cos(0.01583333(t−0)). The second multiplier 228 b mixes thesignal with cosine wave having a phase calculated according tocos(0.0158333(t−T)) where t is time and T is the sample rate of thesignal output by the 44:1 decimator 648. The third multiplier 668 cmixes the signal with cosine wave having a phase calculated according tocos(0.0158333(t−2T)) where t is time and T is the sample rate. Thefourth multiplier 668 d mixes the signal with cosine wave having a phasecalculated according to cos(0.0158333(t−3T)) where t is time and T isthe sample rate. The fifth multiplier 668 e mixes the signal with cosinewave having a phase calculated according to cos(0.0158333(t−4T)) where tis time and T is the sample rate. In the exemplary embodiment, thesamples output by the multipliers 668 a-668 e are accumulated by theaccumulators 672 a-672 e, respectively, for about a 20-minute period,which results in the collection of about 80 samples. The sample fromeach of the accumulators 672 a-672 e is input to a maximum valuefunction 676. The maximum value function 676 then determines which ofthe five samples received from the accumulators 672 a-672 e has thegreatest value and inputs that greatest value to the subtractor 680. Themaximum value function 676 discards the remaining samples.

Similarly, the signal propagating along the second signal branch 667 bis input to multipliers 670 a-670 e. The first multiplier 670 a mixesthe signal with a cosine wave calculated according tocos(0.0175000(t−0)). The second multiplier 670 b mixes the signal with acosine wave calculated according to cos(0.0175000(t−T)), where T is thesampling rate of the signal output by the 44:1 decimator 648. The thirdmultiplier 670 c mixes the signal with a cosine wave calculatedaccording to cos(0.0175000(t−2T)), where T is the sampling rate of thesignal output by the 44:1 decimator 648. The fourth multiplier 670 bmixes the signal with a cosine wave calculated according tocos(0.0175000(t−3T)), where T is the sampling rate of the signal outputby the 44:1 decimator 648. The fifth multiplier 670 b mixes the signalwith a cosine wave calculated according to cos(0.0175000(t−4T)), where Tis the sampling rate of the signal output by the 44:1 decimator 648. Inthe exemplary embodiment, the samples output by the multipliers 670a-670 e are accumulated by the accumulators 674 a-674 e, respectively,for about a 20-minute period, which results in the collection of about80 samples. The sample from each of the accumulators 674 a-674 e isinput to a maximum value function 678. The maximum value function 678then determines which of the five samples received from the accumulators674 a-674 e has the greatest value and inputs that greatest value to thesubtractor 680. The maximum value function 678 discards the remainingsamples. The subtractor then determines the difference between thesamples received from the maximum value functions 676 and 678 andoutputs the difference to the slicer 658.

Alternative embodiments of the heuristically correlated detector 65 arepossible. For example, it can estimate the phases of the signal receivedby the endpoint transceiver more accurately, by mixing the signalpropagating along each of the signal branches with more than five cosinefunctions having the phase of the function increases in smallerincrements. For example, it could increment the phase by about 0.5Trather than about 1T. The heuristically correlated detector also couldestimate the phases of the signal less accurately by mixing signals withfewer cosine functions having the phase function for each cosinefunction increased in greater increments.

Referring back to FIG. 6C, the slicer 658 limits each sample receivedfrom the heuristically correlated detector between two predeterminedamplitude boundaries, which increases the signal-to-noise ratio. In onepossible embodiment, the upper boundary is a voltage level of about +1volts and the lower boundary is voltage level of about −1 volts. In theexemplary embodiment, the slicer 658 reads the sliced samples at about20-minute intervals, although other embodiments will read the slicedsamples at other intervals.

A bit latch 660 is clocked and synchronized with the slicer 658 so thatit is set by the last bit at the same interval at which the slicer 658reads the sliced sample. Again, in the exemplary embodiment, theinterval is about 20 minutes although other embodiments might have otherintervals. Again other embodiments might if the last bit has a positivevalue, the bit latch 660 sets a logical “1”. If the last bit has anegative value, the bit latch 660 sets a logical “0”. The bit output bythe latch 660 is then input to the single board computer 540, whichstores the data in memory.

The signal passed to the second signal branch 646 passes through abandpass filter 661, which in the exemplary embodiment has a pass bandfrom about 15.08333 mHz to about 18.25 mHz. The signal is then passedthrough an absolute value function 662 that rectifies the signal andthrough a low pass filter 664, and through a scaling function 666. Inthe exemplary embodiment, the low pass filter 664 that has a cut offfrequency that is adjustable in the range from about 250 μHz to about1.0 mHz. The cut off frequency is adjusted until the low pass filter 664smoothes the signal being processed and the second DSP 538 outputs asignal strength word that accurately identifies the strength of thesignal being received from the endpoint transceiver 112.

The scaling function 666 scales the amplitude of the signal within thebandwidth defined by the low pass filter 664. In the exemplaryembodiment, it scales the amplitude of the signal by a factor of about9.587×10⁻⁶*(Gain/100), where Gain is the gain of the variable gaindevice 502, 504, or 506 that provides an input for the signal beingprocessed by the scaling function 666. The scaled signal is a binarysignal strength word that corresponds to the strength or amplitude ofthe signal received from the endpoint transceiver 112. The single boardcomputer 540 can selectively obtain the signal strength word.

The signal output by the low pass filter 664 is also input to a faultdetection signal branch 681 that determines whether the substationcontroller 108 fails to receive a signal from the endpoint transceiver112 on that sub-sub channel 406 or whether the signal that it isreceiving is too noisy. The signal passes through a standard deviationfunction 682. The signal has a D.C. bias, and the standard deviationfunction 682 calculates the standard deviation of the signal'samplitude, which varies around the D.C. bias.

The signal output by the standard deviation function is input to a 44:1decimator, which reduces the sampling rate from about 2.93 sps to about0.0667 sps. The signal then passes through a low pass filter 686 thathas a cut off frequency that is adjustable between about 1 μHz to about100 μHz. The cut off frequency is adjusted until the low pass filter 686smoothes the signal being processed and the second DSP 538 outputs asignal strength bit and a noise word that accurately indicates lost andnoisy sub-sub-channels 406, respectively, with a desired degree ofaccuracy.

The signal is then input to a high-limit scaling-function 688 and alow-limit scaling function 690. The high-limit scaling function 688scales the amplitude of the signal by the factor 240*(Gain/100), whereGain is the gain of the variable gain device 502, 504, or 506 thatprovides an input for the signal being processed by the scaling function688. The constant (240 in the exemplary embodiment) used in the scalingfunction 688 is set so that the output of the scaling function 688 isabout 6 sigma. The output of the scaling function 688 is an upper limit.Similarly, the low-limit scaling function 690 scales the amplitude ofthe signal by the factor 120*(Gain/100), where Gain is the gain of thevariable gain device 502, 504, or 506 that provides an input for thesignal being processed by the scaling function 690. The constant (120 inthe exemplary embodiment) used in the scaling function 690 is set sothat the output of the scaling function 690 is about 3 sigma. The outputof the scaling function 690 is a lower limit.

The upper and lower limits are input to LOS detection logic 692, whichcompares the unsealed signal strength word output by the low pass filter664 to the upper and lower limits output by the scaling functions 688and 690. The LOS detection logic 692 outputs a signal strength bitindicating a lost channel if the strength of the signal received on thesub-sub-channel 406, as output by the low pass filter 664, first goesabove the upper limit and then below the lower limit or if the strengthof the signal never goes above the upper limit. The LOS detection logic692 outputs a signal strength bit indicating a signal is being receivedon the sub-sub-channel 406 if the strength of the signal as output bythe low pass filter 664 goes above the upper limit and stays above theupper limit. The LOS detection logic 692 also outputs a signal strengthbit indicating a signal is being received on the sub-sub-channel 406 ifthe strength of the signal as output by the low pass filter 664 goesabove the upper limit and then falls below the upper limit but not belowthe lower limit. The single board computer 540 selectively obtains thebit output by the LOS detection logic 692.

The output of the low pass filter 686 is also input to a bit latch 694,which latches the binary word output by the low pass filter 686. Thevalue of this word is the standard deviation and corresponds to theamount of noise present in the signal received on the sub-sub-channel406. The single board computer 540 selectively obtains the noise wordlatched by the bit latch 694.

The single board computer 540 stores in memory the signal strength wordreceived from the scaling function 666, the signal strength bit outputby the LOS detection logic 692, and the noise word output by the bitlatch 694. If the single board computer 540 does not receive the signalstrength bit from the LOS detection logic 692 and it determines thatthere should be an endpoint transceiver 112 sending a signal on thatparticular sub-sub-channel 406, it can generate an error. In onepossible embodiment, the single board computer 540 can then send acommand to find the missing endpoint transceiver 112. In anotherpossible embodiment, the single board computer 540 can send the signalstrength bit or other data item to the central office 334 eitherindicating a possible failure in the distribution plant or identifyingthe endpoint transceiver 112 as failed so that it can be repaired orreplaced.

Additionally, one can use the signal strength word output by the scalingfunction 666 for diagnostic purposes. For example, if there is a signalstrength word, but the scaled value is not within the predeterminedrange, one might adjust the biasing of the variable gain device 502,504, or 506. In yet another possible embodiment, the single boardcomputer 540 automatically instructs the variable gain device controller528 in the CPLD 530 to adjust the bias of the variable gain device 502.

Other possible embodiments might include different combinations of bitsor binary words output by the LOS detection logic 692. In one possibleembodiment, the LOS detection logic 692 outputs only a single signalstrength bit. In other embodiments, the LOS detection logic 692 outputsbinary words or other combinations of bits and/or flags. Yet anotherpossible embodiment does not include the fault detection signal branch681. This embodiment outputs only the signal strength word from thescaling function 666 and the single board computer 540 uses thisinformation to determine the presence or absence of a signal from theendpoint transceiver 112. Other possible embodiments do not include theseparate signal branch 646 at all.

Again, although an exemplary embodiment of digital signal processinglogic is illustrated and described herein, many other embodiments fordemodulating received signals are possible. For example, thedemodulating and demultiplexing can be performed using any combinationof hardware and/or software and any type of multiplexing/demultiplexingand modulation/demodulation schemes that can simultaneously processsignals received from multiple endpoint transceivers 112.

Each of the parallel sub-sub-channel signal branches is substantiallythe same as the illustrated block diagram for sub-sub-channel 1. Theprimary difference is that the frequency input to the mixer isincremented by about 0.004 Hz for each successive sub-sub-channel 406.The frequency input to the mixer is line locked to the powerdistribution frequency of the 120/240V input for the SPU 332. Similarly,the maximum and minimum cutoff frequencies for the high pass filters 634are increased by about 0.004 Hz for each successive sub-sub-channel 406.Thus, for example, the second sub-sub-channel has a mixer frequency ofabout 0.188 Hz and the high pass filter has a cutoff frequency of about0.202 Hz. In this exemplary embodiment, the one hundred twenty-fifthsub-sub-channel has a mixer frequency of about 0.680 Hz and the highpass filter has cutoff frequency of about 0.694 Hz.

Referring to FIG. 7, when transmitting a signal to the endpointtransceivers 112, the single board computer 540 generates a data packetthat contains a message. The data packet is then buffered by an inputbuffer 700 and a transmit buffer 702, both of which are 60-secondbuffers that hold the data for one minute.

The input and the transmit buffers 700 and 702 form a ping-pongbuffering scheme. The data passes first through the input buffer 700 andthen through the transmit buffer 702. When the data is received at thetransmit buffer 702, it sends a message to the input buffer 700 todelete the data from the input buffer register. This buffering schemeprevents the loss of data.

The data is held in the transmit buffer 702 for about 60 seconds andthen input to the second DSP 538 where it is modulated using a singlechannel, binary frequency shift keying scheme. Specifically, the datapasses through a frequency change function 704. The frequency changefunction 704 determines whether the frequency shifts from one frequencyto another. If the frequency shifts, the frequency change function 704determines that the data bit is a logical “1”. If the frequency does notshift, the frequency change function 704 determines that the data bit isa logical “0”. In the exemplary embodiment, the frequency changefunction determines whether the data bit is a logical “1” or “0”depending on whether the frequency shifts between frequencies of about555 Hz and about 585 Hz.

The data is output from the second DSP 538 and input to a digital toanalog (D/A) converter 710, which outputs a modulated transmit signal toa low pass filter 712. The low pass filter 712 has a cut-off frequencyof about 1.2 KHz and smoothes the modulated transmit signal. Themodulated transmit signal then passes through a variable gain device 714that is electrically isolated by capacitors 716 and 718. The variablegain device 714 is biased by the variable gain device controller 528 ofthe CPLD 530. The variable gain device 714 is biased to set themodulated transmit signal at a predetermined voltage level. In onepossible embodiment, the variable gain device 714 sets the modulatedtransmit signal to a voltage level of about 1.4 Volts RMS.

The modulated transmit signal from the variable gain device 714 is thenamplified. In one exemplary embodiment, the modulated transmit signal isamplified by a power audio amplifier 720 capable of amplifying a signalby about 400 Watts or more. One type of power audio amplifier that canbe used is model K1, which is manufactured by Crown Audio, Inc., ofIndiana, U.S.A. After it is amplified, the modulated transmit signal ispassed through an impedance matching unit 722, and then issimultaneously transmitted onto each of the distribution line conductors302, 304, and 306 through the isolation capacitors 724, 726, and 728,respectively. The modulated transmit signal simultaneously propagatesalong each of the transmission conductors 302, 304, and 306 to each ofthe endpoint transceivers 112.

To prevent insertion loss and distortion of the modulated transmitsignal, the impedance matching unit 722 matches the impedance betweenthe output of the audio power amplifier 720 and the distribution lineconductors 302, 304, and 306. One skilled in the art will appreciatethat the impedance matching unit 722 includes an inductance-capacitancenetwork (not shown).

Although a certain hardware and software configuration for transmittingand processing data signals is illustrated in this exemplary embodiment,there are many possible alternative embodiments and the invention can beembodied in any configuration on hardware and/or software that cantransmit and modulate the transmission signals.

As discussed above, and referring to FIGS. 5 and 8, the modulatedtransmit signal propagates to the 120/240V input for the SPU 332. Thevoltage level is taken from the power supply, conditioned, input to thefourth A/D converter 524, buffered 516 in the fourth buffer programmedinto the CPLD 530, and then input to the first DSP 536.

Within the first DSP 536, the transmit signal is passed through a 50:1decimator, which converts the sample rate of the signal from about500,000 samples per second (sps) to about 10,000 sps. The signal thenpropagates onto two signal branches 801 a and 801 b. Within the firstsignal branch 801 a, the signal first passes through a bandpass filter802 a having a first predefined pass band. In one possible embodiment,the bandpass filter 802 a has a lower cutoff frequency of about 575 Hzand an upper cutoff frequency of about 595 Hz. It isolates signalshaving a frequency of about 585 Hz. In other embodiments, the bandpassfilter 802 a has different bandpasses.

The signal then flows through an absolute value function 804 a, whichrectifies the signal, and then through a low pass filter 806 a, whichhas a cutoff frequency of about 5 Hz. The low pass filter 806 a smoothesthe rectified signal. The rectified signal passes through a 500:1decimator 808 a, which changes the sample rate from about 10,000 sps toabout 20 sps. The signal is then passed from the first DSP 536 to thesecond DSP 538.

The signal passed along the second signal branch 801 b is processed in asubstantially similar method. It flows through a bandpass filter 802 b,an absolute value function 804 b, a low pass filter 806 b, and then a500:1 decimator 808 a. The primary difference from the first signalbranch 801 a is that the bandpass filter 802 b has a second predefinedpass band. In one possible embodiment, the bandpass filter 802 b has alower cutoff frequency of about 545 Hz and an upper cutoff frequency ofabout 565 Hz. It isolates a signal having a frequency of about 555 Hz.In other embodiments, the bandpass filter 802 b has differentbandpasses.

The signal output from each signal branch 801 a and 801 b is input to amax signal function 810, which selects the signal that has the largestamplitude and then passes the larger of the two signals through a lowpass filter 812. The low pass filter 812 further smoothes the signal sothat a steady-state signal strength can be determined. The low passfilter 812 has a cutoff frequency of about 100 mHz. The filtered signalthen is passed through a scaling function 814 that biases the voltagelevel of the signal by a predetermined factor. In one possibleembodiment, the predetermined factor, which equals 1.1×10⁻⁴*(Gain/100),where Gain is the gain of the variable gain device 508.

The scaled signal is input to both a data latch 816 and a loss-of-signal(LOS) detection logic 818. In one possible embodiment, the data latch816 operates in a substantially similar manner as the data latch 668.The LOS detection logic 818 compares signal strength to a predeterminedvalue and outputs a signal strength bit indicating whether the signalstrength is below the predetermined value. Additionally, the data latch816 and the LOS detection logic 818 interface with the single boardcomputer 540 in a substantially similar manner as the data latch 668 andthe LOS detection logic 692. The primary difference is that the singleboard computer 540 uses the output of the data latch 816 and the LOSdetection logic 818 to determine whether the substation controller 108is properly transmitting a signal onto the distribution line 106 asopposed to determining whether a signal is being properly received fromthe endpoint transceiver 112. The data latch 816 and LOS detection logic818 can have similar alternative embodiments as the data latch 668 andthe LOS detection logic 692, respectively.

The signal output from each signal branch 801 a and 801 b also is inputto a bit detection algorithm 820, which determines whether the data bitis a logical “1” or “0”. In one possible embodiment, the bit detectionalgorithm 820, which is programmed into the second DSP 538, receives thesignal output from each signal branch 801 a and 801 b. The bit detectionalgorithm then calculates which signal has a greater amplitude or value.If the signal that has the greater amplitude changes, the bit detectionalgorithm 820 determines that the frequency changed and corresponds to alogical “1” and outputs a high or “1” bit. If the signal that has thegreater amplitude does not change, the bit detection algorithm 820determines that there is not change in the frequency, which correspondsto a logical “0” and outputs a low or “0” bit. The bits output by thebit detection algorithm 820 are input to a buffer 822. In one possibleembodiment, the buffer 822 is a 60-second buffer that accumulates datain one-minute increments and then outputs the data to the flash memory532 where it is stored.

In one possible embodiment, the flash memory 532 stores the datatransmitted by the substation controller 108 for a predetermined periodof time, such as 4.5 days. As new data is stored in the flash memory532, it overwrites oldest data. The data is retrieved from the flashmemory 532 upon receiving a fetch command from the single board computer540. In one possible embodiment, the single board computer 540 generatesa fetch command upon receiving instructions from a user.

Although and exemplary embodiment of digital signal processing logic isillustrated and described herein, many other embodiments for modulatinga data signal for transmission are possible. For example, modulation canbe performed using any combination of hardware and/or software and anytype of modulation scheme that is compatible with the endpointtransceivers 112.

Referring to FIG. 9, the single board computer 540, which has apreemptive operating system, communicates with a control server 934 viaa data communication link 936 such as an Ethernet network. In theexemplary embodiment, the controller server 934 is centrally located inthe central office 334 and communicates with single board computerslocated at several different substations. The control server 934generates commands and forwards them to the single board computer 540.The single board computer 540 then assembles the commands into datapackets, and the substation controller 108 relays the commands to theendpoint transceivers 112. The control server 934 also sends commands tothe single board computer 540 instructing the computer 540 to uploaddata to the control server 934.

The code executed by the single board computer 540 is organized intotasks. In the exemplary embodiment, there are three tasks that controlcommunication with the data communication link 936. These tasks are theCom Serv task 938, the Com Client task 940, and the Net Time task 932.

The control server 934 communicates with the single board computer 540using a metalanguage such as XML. The Com Serv task 938 is a commandprocessor that receives commands and data from the control servers 934.The commands and data that it receives are in XML. The Com Serv task 938then parses the commands into a predetermined data structure that isunderstandable by the operating code executed by the single boardcomputer 540. In the exemplary embodiment, the Com Serv task 938receives and processes all of the commands that communicated from thecontrol server 934 to the single board computer 540.

Additionally, the Com Serv task 938 processes data for uploading to thecontrol server 934 by converting it to XML and then transmitting it tothe control server 934 over the data communication link 936. With theexception of certain data processed and transmitted by the Com Clienttask 940, all of the data transmitted to the Control server 934 isprocessed and transmitted by the Com Serv task 938.

In the exemplary embodiment, the Com Client task 940 converts certaindata to XML and then transmits it to the control server 934. In theillustrated embodiment, the Com Client task 940 processes and transmitsmessages and data that are not specifically requested by the controlserver 934 or otherwise scheduled for period transmission to the controlserver 934. An example includes a message that the status of asub-sub-channel 406 was changed to Lost, indicating that substationcontroller 108 failed to receive a signal from the endpoint transceiver112 assigned or mapped to that sub-sub-channel 406. In one possibleembodiment, the Com Client task 940 reports the Lost status to thecontrol server 934 if the status of the sub-sub-channel is not restoredin a predetermined amount of time. In another embodiment, the Com Clienttask 940 reports the Lost status to the control server 934 as soon asthe Lost status of the sub-sub-channel 406 is generated, which permitsquick identification of failures, including the type and location of theerror. It also permits the quick dispatch of technicians and/orengineers for repair.

The Com Client task 940 also process and transmits messages and datarequested by the control server 934 in certain circumstances. In theexemplary embodiment, the Com Client server 940 processes and transmitsdata that takes more than a significant amount of time to generate whenrequested from the control server 934. An example of such a commandincludes a request by the control server to rebuild the table (discussedherein with respect to the CHAT.DAT data file 916) allocating each ofthe endpoint transceivers 112 to a particular sub-sub channel 406. Inthis exemplary embodiment, a significant amount of time lapses betweenthe time the single board computer 540 requests information or an actionand the time the single board computer 540 responds to the request oracknowledges the action.

The code in the single board computer 540 defines on acommand-by-command basis, whether the Com Serv task 938 or the ComClient task 940 processes and transmits data to the control server 934.In this embodiment, a table stores a list of commands executable by thesingle board computer 540 and identifies either the Com Serv task 938 orthe Com Client task 940 as the task responsible for sending therequested information or acknowledgement of the requested action to thecontrol server 934.

The Net Time task 932 retrieves the current time from a global timeserver that provides an accurate time source. The global time serverretrieves the current time based on Universal Time Coordinated (UTC)from a source such as the Global Positioning System (GPS) or a DCF77signal, which is a radio clock signal generated by an atomic clock. Inthe exemplary embodiment, the global time server is located remotely 102and is connected to the single board computer 540 via the datacommunication link 936. Additionally, the single board computer 540 isprogrammed to adjust the UTC for the time zone served by thedistribution substation 102 and for daylight savings time, if time isadjusted for daylight savings time in the geographic region served bythe distribution substation 102. In an alternative embodiment, theglobal time server is programmed to adjust the UTC for the time zoneserved by the distribution substation 102 and for daylight savings time,if time is adjusted for daylight savings time in the geographic regionserved by the distribution substation 102.

In the exemplary embodiment, the global time server retrieves the UTC ina predetermined interval such as once per day. In turn, the Net Timetask 932 retrieves the time, which is adjusted as appropriate, in apredetermined interval such as once per day. The Net Time task 932 has aclock function that tracks the time and is recalibrated to the timeretrieved from the global time server. In other embodiments, the globaltime server retrieves and adjusts the time more or less frequently thanonce per day and the Net Time task 932 retrieves the time from theglobal time server more or less frequently than once per day. Forexample, the global time server can retrieve the UTC in intervals suchas 5 minutes. Similarly, the Net Time task 932 can retrieve the timefrom the global time server in intervals such as 5 minutes.

The single board computer 540 is also programmed with a plurality oftasks for executing a variety of functions and stored data files. In theexemplary embodiment, these tasks include a CmdExe task 900, a Payloadtask 908, a Work task 912, a Scheduler task 930, CmdEpMon task 902, aCmdEpdWr task 904, a CmdLog task 910, and a CmdFind task 906. Data filesinclude a CHAT.DAT file 914, a FIND.DAT file 916, an ENDPT.DAT file 920,a CHANBITS.DAT file 918, and a SPU.LOG file 928.

The CmdExe task 900 executes all of the tasks received and processed bythe Com Serv task 938. The CmdExe task 900 executes commands requestingdata to be uploaded to the control server 934. The CmdExe task 900 alsoeither executes (or initiates execution of commands by other tasks)requesting a change in the operating parameters of the single boardcomputer 540. Examples include reporting lost endpoint transceiver 112to the control server 934, initiating commands to find a new or a lostendpoint transceiver 112, commands to reassign an endpoint transceiver112 from one sub-sub-channel 406 to another sub-sub-channel 406, andsettings for operating parameters of the first and/or second DSPs 536and 538.

The Payload task 908 interfaces with the CPLD 530 and assembles eachcommand intended for the endpoint transceivers 112 into a data packetthat is decoded by the endpoint transceivers 112. The Payload task 908outputs the data packet to the CPLD 530, which buffers the data 700 and702. The data packet is then transmitted to the endpoint transceivers112 as discussed herein in more detail.

The Work task 912 interfaces with the CPLD 530 and the first and secondDSPs 536 and 538. It sends instructions to the variable gain controller528 to change operating parameters of the first and second digitalsignal processor 536 and 538, such as the gain of the various variablegain devices 502, 504, 506, 508, and 714. It also sends instructions toretrieve log files from the flash memory 532, the updated time base, thesignal strength bits from the scaling function 666 and the data latch816, the signal strength bits corresponding to signal strength from theLOS detection logics 692 and 818, and the noise word from the bit latch694.

The CmdEpdWr task 904 interfaces with and retrieves data from the secondDSP 538 that the endpoint transceivers 112 transmitted. In the exemplaryembodiment, it retrieves the data bit from the bit latch 660 about onceevery 20 minutes. When retrieving the data bit, the CmdEpdWr task 904actually retrieves a bit from the bit latch 660 for the signal receivedfrom each of the three distribution line conductors 302, 304, and 306.It determines which of the distribution line conductors 302, 304, or 306has the strongest signal strength and disregards the bits detected onthe other two distribution line conductors. In the exemplary embodiment,the CmdEpdWr task 904 determines which distribution line conductor 302,304, or 306 has the strongest signal by comparing the signal strengthword output by the scaling function 666 along the signal path 646 of thesecond DSP 538.

After the data bit from the strongest distribution line conductor 302,304, or 306 is selected, the CmdEpdWr task 904 performs an errorcorrection algorithm. In the exemplary embodiment, the CmdEpdWr task 904executes a Bose Chaudhuri Hocquengham (BCH) code to correct errors inthe data bits selected from the bit latch 660. After error correction iscomplete, the data bit is stored in the data fileENDPT.DAT 918.

The CHANBITS.DAT data file 918 stores a table that has a record for eachof the sub-sub-channels 406. In the exemplary embodiment, each record inthe table has an entry identifying the sub-sub-channel 406 to which itcorresponds, the serial number of the endpoint transceiver 112 assignedto the sub-sub-channel 406, and fields to store 63 data bits. Eachendpoint transceiver 112 is assigned a unique identification (I.D.) suchas a serial number that can be formed with numbers, letters, and/or anyother appropriate characters or signature. The data bits received fromeach of the endpoint transceivers 112 are stored in the table in therecord corresponding to the sub-sub-channel 406 over which the data bitwas received.

After 63 data bits are accumulated for a particular sub-sub-channel 406and stored in the table, the CmdEpdWr task 904 assembles the 63 databits into a data packet that includes the serial number of the endpointtransceiver 112 that transmitted the data bits and stores the datapacket in the ENDPT.DAT data file 920. After the data packet is formedand stored in the ENDPT.DAT data file 920, the CmdEpdWr task 904 clearsthe data bits from the table in the CHANBITS.DAT data file 918. In onepossible embodiment, the ENDPT.DAT 920 stores 30 data packets for eachsub-sub-channel 406. In the exemplary embodiment, each data packetcorresponds to about 24 hours worth of data collection, and thus, theENDPT.DAT 920 data file stores 30 days worth of data for each sub-subchannel 406.

The CmdFind task 906 and the CmdEpMon task 902 cooperate to find andmonitor endpoint transceivers 112 that are connected to one of thedistribution line conductors 302, 304, or 306. The CmdFind task 906makes the initial communication with each endpoint transceiver 112 toassign it a base frequency for data transmission to the substationcontroller 108. The base frequency is within the bandwidth of an open orunused sub-sun channel 406.

When a new endpoint transceiver 112 is installed, the control server 934is programmed with the serial number for the new endpoint transceiver112. The command server 934 then sends the serial number and a findcommand to find the endpoint transceiver 112 to the CmdExe task 900 viathe data link 936 and the Com Serv task 938. The CmdExe task 900 passesthe serial number and the find command to the CmdFind task 906, whichidentifies an open sub-sub-channel 406 and maps the serial number to abase frequency within the open sub-sub-channel 406. The CmdFind task 906relays the serial number, assigned or mapped base frequency, and findcommand to the Payload task 908, which assembles this data into a FINDENDPOINT and passes the FIND ENDPOINT data packet to the substationcontroller 108 as described in more detail herein.

The substation controller 108 then transmits the FIND ENDPOINT datapacket downstream on the distribution line conductors 302, 304, and 306and it is processed by the all of the endpoint transceivers 112. Thetransceivers process the FIND ENDPOINT data packet. If the endpointtransceiver 112 has the serial number in the FIND ENDPOINT data packet,it transmits an acknowledge signal to the substation controller 108indicating that it has received its assigned sub-sub-channel 406 andbegins transmitting data to the substation controller 108. If theendpoint transceiver 112 does not have the serial number in the FINDENDPOINT data packet, it discards the FIND ENDPOINT data packet andtakes no further action with respect to the data packet.

The CmdEpMon task 902 monitors the status of each sub-sub-channel 406.It receives the signal strength word output by the scaling function 666,the LOS bit output by the LOS detection logic 692, and the noise wordoutput by bit latch 694. Depending on the output of the LOS detectionlogic 692 and the bit latch 694, the CmdEpMon task 902 changes thestatus of the sub-sub-channel 406 that is being monitored as describedbelow in conjunction with the CHAT.DAT 916 data file.

The CmdFind task 906 and the CmdEpMon task 902 interface with two datafiles, FIND.DAT 914 and CHAT.DAT 916.

The FIND.DAT data file 914 stores information related to the process offinding an endpoint transceiver 112. For example, when ever the CmdFindtask 906 attempts to find and endpoint transceiver 112, it stores in theFIND.DAT data file 914 an I.D. of the find command, or any other commandthat is being sent in the FIND ENDPOINT data packet, the serial numberof the endpoint transceiver 112 it attempting to find, and the frequencyit assigned to the endpoint transceiver 112. The CmdFind task 906 alsostores in FIND.DAT 914 a time stamp indicating when transmission of theFIND ENDPOINT data packet was initiated and a time stamp indicating whenthe substation controller 108 received a reply or acknowledgement fromthe endpoint transceiver 112 that it was attempting to find.

The CHAT.DAT data file stores a database that has a record for eachsub-sub-channel 406. Each record includes a field identifying the basefrequency for the sub-sub-channels 406, the serial number of theendpoint transceiver 112 assigned to that sub-sub-channels 406 (i.e.,base frequency with in the sub-sub-channel 406), and the status of thesub-sub-channel 406 (i.e., base frequency with in the sub-sub-channel406). In the exemplary embodiment, the CHAT.DAT file has 9000 records,each corresponding to one of the 9000 sub-sub-channels 406. In onepossible embodiment, the status assigned to a sub-sub-channel 406selected from the following: Unused, Temporary, Found, Permanent,Blocked, Lost, Restored, and Waiting.

The Unused status is assigned to a sub-sub-channel 406 if it is notassigned to an endpoint transceiver 112. When the CmdFind task 906receives a find command from the control server 934, it identifies asub-sub-channel 406 having an Unused status and assigns the basefrequency within the identified unused sub-sub-channel 406 to the newendpoint transceiver 112. The CmdFind task 906 then inputs the serialnumber, find command, and assigned base frequency to the Payload task908 for processing and down stream transmission.

Upon receiving an acknowledgement from the endpoint transceiver 112, theCmdFind task 906 changes the status of the sub-sub-channel 406 fromUnused to Temporary. The CmdExe task 900 then reports the found statusof the new endpoint transceiver 112 to the control server 934. Uponreporting the Found status of the endpoint transceiver 112, the CmdFindtask 906 changes the status of the assigned sub-sub-channel 406 fromFound to Permanent.

The status of a sub-sub-channel 406 is changed to Blocked to prevent anendpoint transceiver 112 from being assigned that sub-sub-channel 406. Asub-sub-channel 406 can have a Blocked status for a variety of reasons.An example includes detection of a noisy sub-sub-channel 406. If thesingle board computer 540 runs diagnostics and determines that asub-sub-channel 406 is too noisy or if the Control Server 934 sends aninstruction to the substation computer to block out the noisysub-sub-station 406. In the exemplary embodiment, the single boardcomputer 540 compares the value of the noise word received from the bitlatch 694 on the second DSP 538 to a predetermined value, and determinesthat the channel is too noisy if the value of the noise word is greaterthan the predetermined value. The noise word corresponds to the level ofnoise on the sub-sub-channel 406.

If a Blocked status is assigned to a sub-sub-channel 406 that iscurrently being used by an endpoint transceiver 112, the CmdFind task906 will select a new sub-sub-channel 406 that has an Unused status andinstruct the Payload task 908 to generate and initiate transmission of aFIND ENDPOINT data packet. The serial number for the endpointtransceiver 112 is then stored in the record for the newly assignedsub-sub-channel 406 and the status sequences through the Found andPermanent states as described above.

The status of a particular sub-sub-channel 406 is changed to Lost if theCmdEpMon task 902 determines that there is a loss of power at thefrequencies in that sub-sub-channel 406. In the exemplary embodiment,the Work Task 912 receives the signal strength bit from the LOSdetection logic 692 and provides the signal strength bit to the CmdEpMontask 902. If the signal strength bit indicates that the endpointtransceiver 112 assigned to that sub-sub-channel 406 is lost, theCmdEpMon task 902 changes the status of the sub-sub-channel 406 to Lostand the CmdExe task 900 reports the Lost status for the sub-sub-channel406 to the control server 934. The Control Server 934 then typicallyinstructs the CmdFind task 906 to find the lost endpoint transceiver 112assigned to the sub-sub-channel 406. In an alternative embodiment, theCmdFind task 906 automatically attempts to find a lost endpointtransceiver 112.

When a lost endpoint transceiver 112 is found again, the status of theassigned sub-sub-channel 406 is changed from Lost to Restored. Thestatus remains Restored while the Restored status is reported to theControl Server 934 by the CmdExe task 900. The status of thesub-sub-channel 406 is changed from Restored to Permanent upon reportingof the Restored status to the control server 934.

The status of a sub-sub-channel 406 is changed to Wait when the CmdFindtask 906 is instructed to find an endpoint transceiver 112 and thecurrent state of the sub-sub-channel 406 is currently Temporary, Found,Permanent, or Restored. When the status of the sub-sub-channel 406 isWait, the CmdFind task 906 enters a wait state for a predeterminedperiod of time and then instructs the Payload task 908 to generate andtransmit a find packet after the predetermined period of time lapses.Because the signal received from the endpoint transceivers 112 are atlow frequency, they take a while to decay. Given the frequencies used inthe exemplary embodiment, the signal transmitted by the endpointtransceiver 112 can take up to 20 minutes to decay, and thepredetermined period of time in which the CmdFind task 906 sits in thewait state is about 20 minutes or longer.

When an endpoint transceiver 112 is found after the wait state of theCmdFind task 906 lapses, the status of the sub-sub-channel 406 ischanged to Found while the Found status is being reported to the ControlServer 934 and then the status is changed to Permanent after reportingis complete.

The Scheduler task 930 schedules all actions or events that are executedby the single board computer 540 at a predetermined time or in periodicintervals. The Scheduler task 930 schedules and initiates execution of avariety of commands including commands executed internal to thesubstation processing unit 332. For example, the Scheduler task 930instructs the CmdEpdWr 904 to retrieve a data bit from the bit latch 660about once every 20 minutes.

The Scheduler task 930 also schedules the transmission of data packetsto the endpoint transceivers 112. For example, the Scheduler task 930instructs the Payload task 908 to send a TIME data packet to theendpoint transceivers 112 about once every five minutes. The payload forthe TIME data packet includes the current date and time as determined bythe Net Time task 932, which periodically retrieves the current date andtime from the time server and then tracks the current time betweendownload from the time server. If no other data is scheduled fortransmission to the endpoint transceivers 112 on the scheduledone-minute intervals, the Scheduler Task 930 instructs the Payload Taskto send a TIME data packet by default.

An advantage of frequently sending Time data packets to the endpointtransceivers 112 is that it facilitates synchronous operation, includingdata collection, of all the endpoint transceivers that are downstreamfrom the substation controller 108. It also facilitates synchronouscommunication between the substation controller 108 and the endpointtransceivers 112.

In another example and as explained in more detail with respect to theCmdFind task 906, when a new endpoint transceiver 112 is to be installedor a lost endpoint transceiver 112 is being restored, the Scheduler task930 repeatedly instructs the Payload task 908 to send a FIND ENDPOINTdata packet until the new endpoint transceiver 112 acknowledgesassignment of a sub-sub-channel 406. The endpoint transceiver 112acknowledges assignment of a sub-sub-channel 406 by transmitting a datapacket that contains an acknowledgment to the substation controller 108and generating an acknowledgement signal for observation at the endpointtransceiver 112 itself. This repeated transmission of a FIND ENDPOINTdata packet is momentarily interrupted when the interval lapses foranother scheduled transmission of a data packet, such as a TIME datapacket.

In one possible embodiment, the Scheduler task 930 instructs the Payloadtask to send a data packet to the endpoint transceivers 112 once everyminute. An advantage of sending data packets in such short intervalsfacilitates rapid deployment of newly installed endpoint transceivers112. As a result, an installer can receive quick confirmation that theendpoint transceiver 112 was successfully installed without waiting formore than a couple of minutes.

The CmdLog task 910 records each command executed by the single boardcomputer and stores the command in the SPU.LOG text file 928. The CmdLogtask 910 also executes or initiates execution of various diagnostics ofthe single board computer 540 and the first and second DSPs 536 and 538,and records the results of the diagnostics in the SPU.LOG text file 928.

The architecture of the code executed by the single board computer 540has many advantages. For example, it provides a scalable system becauseendpoint transceivers 112 can be quickly added to the system by simplyinstalling the endpoint transceiver 112 and entering the serial numberof the endpoint transceiver 112 into the control server 934. It alsoprovides flexibility for reassigning endpoint transceivers 112 from theSPU 332 located at one distribution substation 102 to another SPU 332located at a different distribution substation 102. For example, ifservice for an endpoint 104 is switched from one distribution substation102 to a different distribution substation 102, the control server 934instructs the single board computer 540 located at the differentdistribution substation 102 to execute a find command for the endpointtransceiver(s) 112 located at the endpoint 104.

Another example occurs when a distribution substation 102 goes offlineand service for all of the endpoints 104 downstream from the offlinedistribution substation 102 are switched to different distributionsubstations 102. In this example, the control server 934 sends findcommands for each of the endpoint transceivers 112 that were originallydownstream from the offline distribution substation 102 to the variousdistribution substations 102 that are still online. The single boardcomputer 540 at the online distribution substations 102 executes thefind commands. The single board computer 540 at each of the onlinedistribution substations 102 then registers the downstream endpointtransceivers 112 for which it executed the find command and from whichit received an acknowledgment.

Additionally, the single board computer 540 and the control server 934cooperate to identify and locate faults in the distribution plant. Inone possible embodiment, for example, when the status of asub-sub-channel is Lost and reported to the control server 934, thecontrol server generates an error report so that a service techniciancan repair or replace the endpoint transceiver 112 assigned to the Lostsub-sub-channel 406. An advantage of automatically reporting the Loststatus of sub-sub-channels 406 is that the utility can identify failuresas quickly as they are reported. Another advantage is that the energyutility can be made aware of the Lost status (whether it due to a failedendpoint transceiver 112 or a loss of power) before a failure is evenreported by a customer and can more quickly take action to repair thefailure than if they had to rely on reports from customers.

Several sub-sub-channels being reported as Lost indicates that there isa failure in the distribution system itself. In another possibleembodiment, if more than one sub-sub-channel 406 has a Lost status, thecontrol server 934 identifies the common points in the distributionsystem that are upstream from the endpoint transceivers 112 assigned tothe Lost sub-sub-channels. Identifying the common points of thedistribution system in the manner helps to identify the potential pointsof the distribution system that failed resulting in a loss of power atthe endpoints. Again, because the single board computer 540 reports theLost status of the sub-sub-channels 406, the control server 934 canquickly and automatically identify a power failure and isolate possiblepoints in the distribution system where the error could have occurred.As a result, technicians and/or engineers can be dispatched to repairthe failure.

In yet another possible embodiment, when some sub-sub-channels 406 havea lost status and other sub-sub-channels 406 do not have a lost status,the control server 934 identifies those points in the distributionsystem that are upstream from the endpoint transceivers 112 assigned tothe Lost sub-sub-channels 406 and not upstream from the endpointtransceivers assigned to the sub-sub-channels 406 that are not Lost.Identifying those points between the endpoint transceivers 112 assignedto the Lost sub-sub-channels 406 and the endpoint transceivers 112assigned to the sub-sub-channels 406 that are not Lost helps the energyutility more accurately isolate areas of the distribution system wherethe failure could be located.

The various embodiments described above are provided by way ofillustration only and should not be construed to limit the invention.Those skilled in the art will readily recognize various modificationsand changes that may be made to the present invention without followingthe example embodiments and applications illustrated and describedherein, and without departing from the true spirit and scope of thepresent invention, which is set forth in the following claims.

What is claimed is:
 1. A system for receiving and processing a pluralityof signals received from a plurality of different customer-basedendpoints within a three-phase power distribution system, thethree-phase power distribution system comprising: the plurality ofdifferent customer-based endpoints respectively located at customersites in an area served by at least one power distribution substation,each endpoint of the plurality of different customer-based endpointsincluding an endpoint transmitter in an electrical communication withpower distribution lines within the three-phase power distributionsystem a three-phase power line coupler; a substation receiver in theelectrical communication with the three-phase power line coupler; and asubstation circuit in the electrical communication with the substationreceiver, the substation circuit configured to simultaneously demodulatethe plurality of signals concurrently received from the plurality ofdifferent customer-based endpoints by separating a channel on the powerdistribution lines carrying the plurality of signals into respectivesignal processing signal paths associated with different ones of theplurality of different customer-based endpoints which are configured tobe located at the customer sites, each of the respective signalprocessing signal paths having a different respective bandwidth.
 2. Thesystem of claim 1 wherein the substation circuit is part of the powerdistribution substation located remotely from facilities at which theplurality of customer-based endpoints are situated; power is provided tothe plurality of customer-based endpoints from the power distributionsubstation via the power distribution lines, and wherein the substationcircuit is programmed to demodulate the plurality of signals usingfrequency shift keying; each of the power distribution lines including arespective conductor of a plurality of conductors for each of aplurality of three phase power line couplers; and the substationreceiver is configured to receive respective signals from the differentones of the plurality of different customer-based endpoints overdifferent ones of the conductors.
 3. The system of claim 2 wherein thesubstation circuit is programmed to demodulate the plurality of signalswithin the range of about 970 Hz to about 1006 Hz.
 4. The system ofclaim 3 wherein each signal of the plurality of signals has a bandwidthof about 10 MHz or less.
 5. The system of claim 4 wherein said eachsignal of the plurality of signals has a bandwidth of 4 MHz.
 6. Thesystem of claim 2 wherein the substation circuit is programmed tosimultaneously demodulate up to 9000 signals, each signal of the 9000signals being from a different customer-based endpoint.
 7. The system ofclaim 1 wherein the substation circuit includes a digital signalprocessor programmed to simultaneously demodulate the plurality ofsignals received from the endpoint transmitter.
 8. The system of claim 1wherein the substation receiver simultaneously receives signals fromrespective transceivers in the plurality customer-based endpoints. 9.The system of claim 1 wherein the three-phase power line coupler is inthe electrical communication with a power distribution line of the powerdistribution lines within the power distribution system, the powerdistribution system further comprising one or more of the customer-basedendpoints in the electrical communication within the power distributionsystem, each endpoint including: an endpoint circuit configured togenerate data; and the endpoint transmitter in the electricalcommunication with the endpoint circuit and the power distribution linewithin the power distribution system, said each endpoint configured togenerate a modulated signal embodying the modulated signal, to modulatethe data using frequency shift keying, and to transmit the modulatedsignal onto the power distribution line.
 10. The system of claim 9wherein: the endpoint circuit includes an automated meter readingdevice, the automated meter reading device being interfaced with anelectrical meter; and the data includes a quantity of electrical powermeasured by the electrical meter.
 11. The system of claim 9 wherein theendpoint transmitter is integrally formed in a customer-based endpointof said one or more of the customer-based endpoints.
 12. A method ofprocessing a plurality of signals received from a plurality of differentcustomer-based endpoints, the method comprising: respectively locatingat customer sites in an area served by at least one power distributionsubstation, each endpoint including an endpoint transmitter inelectrical communication with power distribution lines; concurrentlyreceiving the plurality of signals from a power distribution line of thepower distribution lines, each signal of the plurality of signalscorresponding to a different frequency bandwidth; and demodulating theplurality of signals by separating a channel on the power distributionlines carrying the plurality of signals into respective signalprocessing signal paths associated with different ones of the pluralityof different customer-based endpoints which are configured to be locatedat the customer sites, each of the respective signal processing signalpaths having a respective different frequency bandwidth.
 13. The methodof claim 12 wherein said demodulating the plurality of signals includesdemodulating said each of the signals using frequency shift keying, andwherein the different frequency bandwidth is predetermined frequencybandwidth.
 14. The method of claim 13 wherein obtaining the plurality ofsignals from the power distribution line includes obtaining up to 9000signals.
 15. The method of claim 12, wherein the power distribution lineis a three-phases power distribution line having a respective conductorfor each of the three phases, and further comprising simultaneouslyreceiving the plurality of signals from said each of the endpoints; andmitigating signal bleed in transmitting of a control signal to theplurality of different customer-based endpoints by transmitting thecontrol signal over each of a plurality of conductors for the threephases with a different phase.
 16. A system for receiving and processinga plurality of signals received from a plurality of differentcustomer-based endpoints respectively located at customer sites in anarea served by at least one power distribution substation, each endpointincluding an endpoint transmitter in an electrical communication withpower distribution lines within a three-phase power distribution system,the power distribution system comprising: a three-phase power linecoupler including a three-phase power-line transformer respectivelycoupling power to a line of the power distribution lines, the line ofthe power distribution lines having a respective conductor for each ofthree phases of the three-phase power line coupler; an interface forcommunicating data with a utility central office; a substation receiverin the electrical communication with the three-phase power line coupler;and a substation circuit in the electrical communication with thesubstation receiver, the substation circuit configured to simultaneouslydemodulate the plurality of signals concurrently received from theplurality of different customer-based endpoints by separating a channelon the power distribution lines carrying the plurality of signals intorespective signal processing signal paths associated with different onesof the plurality of different customer-based endpoints; and mitigatesignal bleed in transmitting of a control signal to the plurality ofdifferent customer-based endpoints by transmitting the control signalover each of a plurality of conductors for the three phases of thethree-phase power line coupler with a different phase.
 17. The method ofclaim 12 wherein obtaining the plurality of signals from the powerdistribution line includes obtaining the plurality of signals within afrequency range from about 970 Hz to about 1006 Hz.
 18. The method ofclaim 17 wherein said obtaining the plurality of signals from the powerdistribution line further includes obtaining the plurality of signals,said each of the plurality of signals having a bandwidth of about 10 MHzor less.
 19. The method of claim 12 wherein obtaining the plurality ofsignals from the power distribution line includes obtaining theplurality of signals, said each of the plurality of signals having abandwidth of about 4 MHz.
 20. The system of claim 16, wherein thesubstation circuit is further configured to transmit the control signalby transmitting three control signals separated from each other in phaseby 120 degrees over respective ones of the conductors.
 21. The system ofclaim 16, wherein the substation receiver is configured and arranged toreceive the control signal transmitted by the substation circuit via thepower distribution lines; and the substation receiver is configured andarranged to record the control signal.
 22. The system of claim 16,wherein for said each of the conductors, the substation receiver has arespective input terminal set connected to the respective conductor by arespective current path through a respective first current transformerand a respective second current transformer.